THE ASCENT OF MAN
JACOB BROWNOWSKI
MACDONALD FUTURA PUBLISHERS 1973
PART IX
Chapter 9: The Ladder of Creation
The theory of evolution by natural selection was put forward in the 1850s independently by two men. One was Charles Darwin; the other was Alfred Russell Wallace. Both men had some scientific background, of course, but at heart both men were naturalists.
- The fact is that there are two traditions of explanation that march side by side in the ascent of man. One is the analysis of the physical structure of the world. The other is the study of the processes of life: their delicacy, their diversity, the wavering cycles from life to death in the individual and in the species.
- And these traditions do not come together until the theory of evolution; because until then there is a paradox, which cannot be resolved, which cannot be begun, about life.
The paradox of the life sciences, which makes them different in kind from physical science, is in the detail of nature everywhere. We see it about us in the birds, the trees, the grass, the snails, in every living thing. It is this. The manifestations of life, its expressions, its forms, are so diverse that they must contain a large element of the accidental. And yet the nature of life is so uniform that it must be constrained by many necessities.
So it is not surprising that biology as we understand it begins with naturalists in the 18th and 19th centuries: observers of the countryside, bird-watchers, clergymen, doctors, gentlemen of leisure in country houses. I am tempted to call them, simply, ‘gentlemen in Victorian England’, because it cannot be an accident that the theory of evolution is conceived twice by two men living at the same time in the same culture – the culture of Queen Victoria in England.
- Charles Darwin was in his early twenties when the Admiralty was about to send out a survey ship called the Beagle to map the coast of South America, and he was offered the unpaid post of naturalist.
- The five years he spent on that ship transformed Darwin. He came home convinced that species are taken in different directions when they are isolated from one another; species are not immutable.
- But when he came back he could not think of any mechanism that drove them apart. That was in 1836.
When Darwin did hit on an explanation for the evolution of species two years later, he was most reluctant to publish it. He might have put it off all his life if a very different kind of man had not also followed the same steps of experience and thought that moved Darwin, and arrived at the same theory. He is the forgotten and yet the vital character, a sort of man from Porlock in reverse, in the theory of evolution by natural selection.
His name was Alfred Russel Wallace, a giant of a man with a Dickensian family history as comic as Darwin’s was stuffy. At that time, in 1836, Wallace was a boy in his teens; he was born in 1823, and that makes him fourteen years younger than Darwin. Wallace’s life was not easy even then.
- He took up the profession of land-surveying, which did not require a university education.
Evidently it was an open-air life, and Wallace became interested in plants and insects. When he was working at Leicester, he met a man with the same interests who was rather better educated. His new friend astonished Wallace by telling him that he had collected several hundred different species of beetles in the neighborhood of Leicester, and that there were more to be discovered.
- It was a revelation to Wallace, and it shaped his life and his friend’s. The friend was Henry Bates, who later did famous work on mimicry among insects.
When he was twenty-five, Wallace decided to become a full-time naturalist. It was an odd Victorian profession. It meant that he would have to keep himself by collecting specimens in foreign parts to sell to museums and collectors in England. And bates would come with him. so the two of them set off in 1848 with £100 between them. They sailed to South America, and then a thousand miles up the Amazon to the city of Manaus, where the Amazon is joined by the Rio Negro.
- It turned out that the Indians were not fierce but helpful. Wallace drew them into the business of collecting specimens.
Sooner or later, amid the pleasures and the labours of the forest, the burning question began to flicker in Wallace’s acute mind. How had all this variety come about, so alike in design and yet so changeable in detail? Like Darwin, Wallace was struck by the differences between neighbouring species, and like Darwin he began to wonder how they had come to develop so differently.
- Wallace was as acute an observer of men as of nature, and with the same interest in the origin of differences. He was perhaps the first person to seize the fact that the cultural distance between the civilization of the Amazon ‘savages’ and ours is much shorter than we think. He returned from the tropics convinced that related species diverge from a common stock.
We feel that Darwin would really have like to die before he published the theory, provided after his death the priority should come to him. That is a strange character. It speaks for a man who knew that he was saying something deeply shocking to the public (certainly deeply shocking to his wife) and who was himself, to some extent, shocked by it. The hypochondria (yes, he had some infection from the tropics to excuse it), the bottles of medicine, the enclosed, somewhat suffocating atmosphere of his house and study, the afternoon naps, the delay in writing, the refusal to argue in public: all those speak for a mind that did not want to face the public.
The younger Wallace, of course, was held back by none of these inhibitions. Brashly he went off in spite of all adversities to the Far East in 1854, and for the next eight years traveled all over the Malay archipelago to collect specimens of the wild life there that he could sell in England. By now he was convinced that species are not immutable; he published an essay On the Law which has regulated the Introduction of New Species in 1855; and from then ‘the question of how changes of species could have been brought about was rarely out of my mind’.
- In February of 1858 Wallace was ill on the small volcanic island of ternate in the Moluccas, the Spice Islands between New Guinea and Borneo.
- And there, on a ight of fever, he recalled the same book by Malthus and had the same explanation flash on him that had struck Darwin earlier.
- Darwin received Wallace’s paper in his study four months later, on 18 June 1858. he was at a loss to know what to do.
- Friends arranged that Wallace’s paper and one by Darwin should be read in the absence of both at the next meeting of the Linnean Society in London the following month.
- The papers made no stir at all. But Darwin’s hand had been forced. He wrote The Origin of Species and published it at the end of 1859, and it was instantly a sensation, and a best seller.
The theory of evolution by natural selection was certainly the most important single scientific innovation in the 19th century. When all the foolish wind and wit that it raised had blown away, the living world was different because it was seen to be a world in movement. The creation is not static but changes in time in a way that physical processes do not. The physical world ten million years ago was the same as it is today, and its laws were the same. But the living world is not the same; for example, ten million years ago there were no human beings to discuss it. Unlike physics, every generalization about biology is a slice in time; and it is evolution which is the real creator of originality and novelty in the universe.
- If that is so, then each one of us traces his make-up back through the evolutionary process right to the beginnings of life.
- When we look back for the common origin of life, today we look even more deeply, at the chemistry that we all share.
- The blood in my finger has come by some millions of steps from the very first primeval molecules that were able to reproduce themselves, over 3,000 million years ago, depending in part on heredity and in part on chemical structure.
- Explanations picture the species separating one after another, in successive stages – that is implied when the theory of evolution is accepted. And from that moment it was no longer possible to believe that life could be re-created at any time now.
- When the theory implied that some animal species came into being more recently than others, critics most often replied by quoting the Bible. Yet most people believed that creation had not stopped with the Bible.
Fables about creatures that come to life spontaneously are very ancient and are still believed, although Louis Pasteur disproved them beautifully in the 1860s. He did much of that work in his boyhood home in Arbois in the French Jura which he loved to come back to every year. He had done work on fermentation before that, particularly the fermentation of milk (the word ‘pasteurization’ reminds us of that). But he was at the height of his power in 1863 (he was forty) when the Emperor of France asked him to look into what goes wrong with the fermentation of wine, and he solved the problem in two years. It is ironic to remember that they were among the best wine years that have ever been; to this day 1864 is remembered as being like no other year.
‘The wine is a sea of organisms,’ said Pasteur. ‘By some it lives, by some it decays.’ There are two things striking in that thought. One is that Pasteur found organisms that live without oxygen. At the time that was just a nuisance to wine-growers; but since then it has turned out to be crucial to the understanding of the beginning of life, because then the earth was without oxygen. And second, Pasteur had a remarkable technique by which he could see the traces of life in the liquid. In his twenties he had made his reputation by showing that there are molecules that have a characteristic shape. And he had since shown that this is the thumbprint of their having been through the process of life.
- Right hand, left hand; that was the deep clue that Pasteur followed in his study of life. The world is full of things whose right-hand version is different from the left hand version – a corkscrew, a snail, the hands. They can be mirrored in one another but they are not interchangeable.
- This is true of some crystals whose facets are so arranged that there are right-hand versions and left-hand versions. Pasteur hit on the notion that there must be right-handed and left-handed molecules too.
- A solution of crystals all of one shape will behave unsymmetrically towards an unsymmetrical beam of light. As the polarizing disc is turned, the solution will look alternatively dark and light.
The remarkable fact is that a chemical solution from living cells does just that. We still do not know why life has this strange chemical property. But the property establishes that life has a specific chemical character, which has maintained itself throughout its evolution. For the first time Pasteur had linked all forms of life with one kind of chemical structure. From that powerful thought it follows that we must be able to link evolution with chemistry.
The theory of evolution is no longer a battleground. That is because the evidence for it is so much richer and more varied now than it was in the days of Darwin and Wallace.
- The most interesting and modern evidence comes from our body chemistry. Let me take a practical example: I am able to move my hand because the muscles contain a store of oxygen, put there by the protein myoglobin, made up of over 150 amino acids. The number is the same in me and in all other animals that use myoglobin.
- But the amino acids are slightly different. Between me and the chimpanzee there is just one difference but with the bush baby there are several differences. Between me and the sheep and the mouse, the number of differences increases.
- It is the number of amino acid differences which is a measure of the evolutionary distance between me and the other mammals.
- 4,000 million years ago the atmosphere was expelled from the interior of the earth – a cauldron of steam, nitrogen, methane, ammonia and other reducing gases, as well as carbon dioxide, but there was no free oxygen, because oxygen is produced by plants.
- Around 1950 Stanley Miller put that atmosphere in a flask, simulated lightning, exposed it to ultra violet-light and other violent forces and formed amino acids. From them the proteins are made, and proteins are the constituents of all living things.
We used to think, until a few years ago, that life had to begin in those sultry, electric conditions. And then it began to occur to a few scientists that there is another set of extreme conditions which may be as powerful: that is the presence of ice. It is a strange thought: but ice has two properties which make it very attractive in the formation of simple, basic molecules. First of all, the process of freezing concentrates the material, which at the beginning of time must have been very dilute in the oceans. And secondly, it may be that the crystalline structure of ice makes it possible for molecules to line up in a way which is certainly important at every stage of life.
- Biology has been fortunate in discovering two great and seminal ideas – the theory of evolution by natural selection and how to express the cycles of life in a chemical form that links them with nature as a whole.